Many radiation detectors, such as a Focal Plane Array (FPA) of infra-red (IR) radiation detectors, and Laser Radar (LADAR), output a current that must be amplified prior to signal processing. The Capacitive Transimpedance Amplifier (CTIA) is one conventional circuit that is often used for this purpose. By example, reference can be had to U.S. Pat. No. 4,786,831 entitled “Integrating Capacitively Coupled Transimpedance Amplifier”, by Arthur L. Morse, Steven D. Gaalema, Ingrid M. Keimel, and Mary J. Hewitt, the disclosure of which is incorporated by reference herein in its entirety.
FPAs are typically comprised of a two-dimensional array of monolithic IR detectors. The individual detectors may be organized in a regular row and column, mosaic-type fashion. Such an array of detectors may be comprised of, as examples, HgCdTe, InSb, GaAs or doped silicon semiconductor material. The IR induced signal from each of the IR detectors is typically coupled to FPA readouts, such as a CTIA, a source follower direct readout, or a charge coupled device, where the signals are integrated over an interval of time and subsequently read out by a suitable multiplexing means.
FPA readouts are preferably constructed to exhibit low device and circuit noise characteristics for obtaining a satisfactory signal-to-noise ratio. The readouts preferably also consume low power to achieve both weight and size reduction. Readouts chips may be coupled to, or “bumped”, with detector arrays using indium bump technology.
The capacitive feedback trans-impedance amplifier circuit (CTIA), is utilized in infrared and other sensing applications to integrate the current from a detector for a specified period of time. Also, the CTIA provides a stable detector bias voltage that is independent of detector current, produces a very linear signal response to input current, and has adequate signal bandwidth. However, in the design of a CTIA circuit, wide bandwidth operation and low power consumption are usually conflicting requirements.